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(EX2/4) Effect of Variation in Equilibrium Shape on ELMing H-mode Performance in DIII-D Diverted Plasmas

M. E. Fenstermacher¹⁾, T. H. Osborne²⁾, T. W. Petrie²⁾, C. J. Lasnier¹⁾, A. W. Leonard²⁾, J. G. Watkins³⁾, T. N. Carlstrom²⁾, R. J. Groebner²⁾, A. W. Hyatt²⁾, R. J. La Haye²⁾, M. A. Mahdavi²⁾, G. D. Porter¹⁾, S. L. Allen¹⁾, J. A. Boedo⁴⁾, N. H. Brooks²⁾, R. J. Colchin⁵⁾, R. Maingi⁵⁾, M. E. Rensink¹⁾, T. L. Rhodes⁶⁾, D. M. Thomas²⁾, M. R. Wade⁵⁾, W. P. West²⁾, D. G. Whyte⁴⁾, N. S. Wolf¹⁾, the DIII-D Team^2)
 
1) Lawrence Livermore National Laboratory, Livermore, California
²⁾ General Atomics, San Diego, California
³⁾ Sandia National Laboratories, Albuquerque, New Mexico
⁴⁾ University of California-San Diego, La Jolla, California
⁵⁾ Oak Ridge National Laboratory, Oak Ridge, Tennessee
⁶⁾ University of California-Los Angeles, Los Angeles, California

Abstract.  The changes in the performance of the core, pedestal, scrape-off-layer (SOL), and divertor plasmas as a result of changes in triangularity, $\delta$, up/down magnetic balance, and secondary divertor volume were examined in shape variation experiments using ELMing H mode plasmas on DIII-D. In moderate density, unpumped plasmas, high $\delta$ $\sim$ 0.7 increased the energy in the H mode pedestal and the global energy confinement of the core, primarily due to an increase in the margin by which the edge pressure gradient exceeded the value which would have been expected had it been limited by infinite-n ideal ballooning modes. In addition, a nearly balanced double-null (DN) shape was effective for sharing the peak heat flux in the divertor in these attached plasmas. For detached plasmas good heat flux sharing was obtained for a substantial range of unbalanced DN shapes. Finally, the presence of a second X-point in unbalanced DN shapes did not degrade the plasma performance if it was sufficiently far inside the vacuum vessel. These results indicate that a high $\delta$ unbalanced DN shape has some advantages over a single null shape for future high power tokamak operation.

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